Fish attracting apparatus



FIG. 5

FREQUENCY, c/ 5 POWER AMPLIFIER A 24 TIME, SECONDS FIG. 6

J. D. RICHARD ETAL FISH ATTRACTING APPARATUS Filed July 12, 1967 OSCILLATOR l 7OO c/s NOISE GENERATOR BAND'PASS F LTOR AMPLIFIER Dec. 3, 1968 MAJb I/MM FIG.

S R o T N E V N United States Patent 3,414,873 FISH ATTRACTING APPARATUS Joseph D. Richard, 3613 Loquat Ave., Miami, Fla. 33133, and Warren J. Wisby, 600 Roosevelt Blvd., Falls Church, Va. 22044 Continuation-in-part of application Ser. No. 454,418, May 10, 1965. This application July 12, 1967, Ser. No. 652,793

5 Claims. (Cl. 340-5) ABSTRACT OF THE DISCLOSURE An apparatus for attracting predatory fish by means of pulsed low frequency acoustic signals transmitted into the ocean. Acoustic noise pulses having frequency components predominently in the low audio and sub-audio portions of the spectrum are transmitted. The frequency content, modulation, and repetition characteristics of the transmitted acoustic pulses closely simulate the turbulence and vibratory sounds generated by injured or struggling fish.

This application is a continuation-in-part of our (:0- pending application Ser. No. 454,418 filed May 10, 1965, and now abandoned.

This invention relates generally to a method and apparatus for attracting predatory fish by means of pulsed acoustic noise signals transmitted into the ocean.

In the past, fishermen have employed several basic techniques for attracting fish. These have been almost entirely confined to visual and olfactory attractants. The former has the disadvantage of a very short range of influence due to the generally poor transparency of sea water. The latter has two disadvantages. Because of the slow rate of diffusion, the area of influence of the olfactory attractant extends only downstream. Furthermore, the maintainence of an olfactory attractant, usually called a chum line, over long periods of time involves not only the expenditure of a large quantity of bait but also a considerable physical effort.

It is well known that sound is transmitted very well in water. It is also known that fish hear and are able to use this sensory capability to detect and localize the source of mechanical disturbances underwater such as those generated by other fish when in motion.

It is generally believed that fish sense the pressure component of an acoustic signal with the labyrinth structure and sense the particle displacement component of an acoustic signal with the lateral line organs. These lateral line organs are particularly important for the detection and localization of mechanical disturbances within the near field (within one wavelength of the source) where the particle displacements are disproportionately large compared to the pressure signal.

The present invention provides apparatus for attracting fish by means of an acoustic attractant. Low frequency noise signals are pulsed and transmitted into the ocean as acoustic singals. These pulsed acoustic signals simulate the turbulence sounds and pressure fluctuations generated by spasmotically moving (such as injured or struggling) fish. It has been discovered by the applicants that many species of predatory fish are attracted by such sounds. Experiments were conducted to determine the fundamental frequencies of these fish movements. These frequencies were found to lie in a band from c./s. to around 100 c./s. Furthermore, these same frequencies, when simulated by the subject apparatus, were found to be very effective in attracting predatory fish. Our original patent application, referred to above, described apparatus for attracting fish by means of acoustic pulses having frequency components confined to these low fequencies.

Patented Dec. 3, 1968 a significant extent by the harmonics of the fundamental tail beat frequencies extending out to at least the third odd harmonic of the highest frequency mentioned in our original application. The third odd harmonic is 700 c./s. for a fundamental frequency of c./s. Although these harmonics might be thought of as being less significant biologically to the fish, their hearing sensitivity rises rapidly above 100 c./s. (peaking somewhere between 300 c./s. and 600 c./s. depending on the species) so that it 'is likely that at least some of these harmonics are perceived more acutely than are the fundamental frequencies. Therefore, although predatory fish are most effectively attracted by pulsed acoustic signals of the character described previously within the frequency range 10 c./s. to 100 c./s., they are also effectively attracted by frequencies which simulate the upper harmonics of these fundamental frequencies extending to at least 700 c./s.

It is the principal object of the present invention to provide a means for attracing fish which is devoid of the disadvantages mentioned above and which is, at the same time, entirely practical and otherwise suitable for commercial fishery application.

It is a further object of the present invention to provide a means for attracting fish from much greater distances than heretofore possible.

A further object of the present invention is to provide an acoustic fish attracting means based on scientific theory which has been thoroughly verified experimentally The acoustic attractant signal directly simulates the mechanical waves radiated into the Water by a wounded or otherwise struggling prey fish and is effective in attracting predatory fish from distances out to at least a few hundred meters.

Other objects and advantages of the present invention will become more apparent from a study of the following specifications and drawings in which:

FIGURE 1 shows a block diagram and schematic view of fish attracting apparatus according to the present invention.

FIGURE 2 shows an alternate schematic arrangement for providing suitable acoustic pulses.

FIGURE 3 shows a photoconductive switch as an alte nate means for switching the electrical signal.

FIGURE 4 shows the frequency spectra of typical pulses from a filtered noise generator.

FIGURE 5 shows the frequency spectrum of pulses from a harmonic generator.

FIGURE 6 shows the time sequence of two typical pulse series.

Referring again to FIGURE 1, a noise generator 1 is shown having a wide band noise output fromabout 10 c./s. to 700 c./s. Typical noise generators have a random output having a uniform amplitude distribution extending well into the ultrasonic range, but for the present application only the portion of the frequency spectrum below 700 c./s. is required. A filter 2 is used to reduce the noise band to the desired frequency range. The switch 8 is used to select either a noise signal from the noise generator 1 or else a square Wave signal from the oscillator 5. The square wave output is obtained from a sine wave signal by overdriving an amplifier stage within the oscillator 5 in the conventional manner. As an alternative, a free running multivibrator or other suitable pulse generator may be used as a harmonic generator. The cam switch 3-6 is driven by the motor 7 so that electypical trical pulses are intermittently passed to the power amplifier 4. The motor 7 drives the cam switch 6 at 12 r.p.m. so that the pulse sequence is continuously repeated. The electrical pulses are amplified by the power amplifier 4 and passed down the electrical cable 10 to the electroacoustic transducer (sound projector) 9 which is suspended above the ocean bottom 37. The sound projector 9 transmits acoustic pulses into the surrounding water which correspond to the aforementioned electrical pulses. The sound projector 9 generates acoustic signals underwater at least over a portion of the frequency range 10 c./s. to 700 c./ s. in response to a suitable output from the amplifier 4. Ideally the sound projector should have substantial response over the entire frequency range mentioned above. However, sound projectors having a considerably narrower frequency response have also been used with considerable success. It may be seen therefore that acoustic pulses may be transmitted from the sound projector 9 which correspond to the pulsed electrical output of either the overdriven oscillator or the noise generator 1 (as modified by the filter 2).

In FIGURE 2 a partially transparent optical disk 19 is shown having two photographic sound tracks such as the sound track 22. These sound tracks are similar in operation to the well known optical sound tracks on motion picture film except that the disk configuration results in the continuous repetition of the output signal. The optical disk 19 is rotated at 12 r.p.m. by the motor 21. The optical density variations of the sound track 22 correspond to pulsed electrical signals having frequency components within the range c./s. to 700 c./s. when the disk 19 is rotated by the motor 21. Electrical signals are derived from the sound track by passing light from the light source 20 through the sound track 22 onto photo-resistor 18. Variations in light falling upon the photo-resistor 18 result in corresponding voltage variations at the point 23 from current supplied by the battery 17. Thus a voltage signal derived from the sound track 22 is fed into the power amplifier 24 and a corresponding acoustic signal is transmitted into the water by the sound projector 25.

FIGURE 3 shows a photoconductive switch arrangement which is preferable to the mechanical switch shown in FIGURE 1. The photoconductive switch allows the selected electrical signal to be switched on and off without generating undesired transient pulses. When the switch is closed, the incandescent lamp 14 is illuminated by current from the battery 16. The lamp 14 and a photoconductive resistor 13 are enclosed together in a light proof housing. The electrical resistance of the photoconductive resistor 13 is typically greater than 10 ohms under dark conditions. When the lamp 14 is illuminated, however, the electrical resistor 13 is reduced to typically less than a few hundred ohms. Because of the thermal time constant of the filament in the lamp 14, the resistance of the photoconductor 13 does not change abruptly in a stepwise manner but might require from 10 to 500 milliseconds (depending on the particular type of lamp used) to change from the maximum to minimum value of resistance. The same gradual transition takes place when the lamp 14 is switched off and the electrical resistance of the photoconductor 13 returns to its normal high value. A signal at the input 11 of the photoconductive switch appears at the output 12 only when the lamp 14 is luminated. Pulses having faster rise times may be obtained by the use of photoconductive switches having faster response times or by other types of switching circuits.

FIGURE 4 shows the frequency spectrum 27 of a typical acoustic signal transmitted into the water by the sound projechr 9 when the noise generator 1 is used as a signal source. The pressure spectrum levels above .0002 dyne/cm. are shown as measured at a distance of one meter from the projector 9. The acoustic signal has a peak spectrum level of about 95 db over the octave band 25 c./s. to 50 c./s. and falls off at about 24 db per octave above and below these limits, The acoustic signal output level may be varied. For example, an alternate peak level of about db is shown by the noise spectrum 29. Typical ocean ambient noise spectrum levels 30 are also indicated. Alternatively, other frequency bands, either narrower or wider than the octave bands shown, may be selected by the band-pass filter 2. Although pulsed low frequency noise signals have proven to be most effective for attracting predatory fish, higher frequency signals typified by the noise spectrum 28, may also be used effectively for at least some fish species. Although it is preferable to emphasize the most effective portions of the noise spectrum by the use of the filter 2 as shown in FIGURE 1, it is also possible to attract some fish species, particularly sharks, by the transmission of a broad band noise signal as would be obtained by excluding the band-pass filter 2 entirely.

FIGURE 5 shows the frequency spectrum of a typical acoustic signal transmitted into the water by the sound projector 9 when the oscillator 5 (having a square wave output) is used as a signal source. The acoustic signal consists of a fundamental frequency 32 of 40 c./s. along with a series of odd harmonics. The square wave electrical signal is generated in the conventional manner by overdriving a sine wave signal into an amplifier stage within the oscillator 5. As a alternative, a multivibrator type oscillator may be used to generate square waves having a suitable harmonic content. Square wave signals having fundamental frequencies below c./s. are preferred. Very low square wave frequencies having fundamentals down to around 5 c./ s. are effective if the signal is passed through an equalization network to emphasize the higher harmonics which are derived from the fundamental frequency. It is also possible to attract fish with signals having fundamental frequencies higher than 100 c./s. (even as high as 500 c./s., or higher) but generally such signals are less effective because only a relatively few of the harmonies of such high fundamental frequencies are audible to the fish. Narrow band, harmonic free signals, such as pure sine waves, are usually not effective for attracting fish.

FIGURE 6 shOWS two typical pulse sequences 35 and 36 suitable for attracting fish. The pulse sequence 35 is obtained from the optical sound track 22 shown in FIGURE 2. The pulse sequence 36 is obtained from the cam switch 36 shown in FIGURE 1. Other pulsing techniques may be used as alternatives to those shown. For example, the broad band noise signals may be manually pulsed or else played back from magnetic tape recordings. Wide variations in pulse repetition rate and duty cycle have been found to be effective. Some fish species respond best to a rapid and almost continuous sequence of short pulses typified by the pulse sequence 35. Other species respond best to a lower pulse repetition rate having at least occasional quiet periods between pulses typified by the pulse sequence 36.

Thus we have described a method and apparatus for attracting predatory fish by means of acoustic pulses transmitted into the ocean. The apparatus described herein has been proven effective for attracting many species of predatory fish including groupers, Snappers, sharks, and others from distances of at least a few hundred meters and probably out to 500 meters or beyond. Broad band random noise signals, square wave signals, or other suitable broad band electrical waveforms are given as examples of a signal source. Various means are described for modulating the amplitude or otherwise pulsing these noise signals. Acoustic pulses corresponding to the pulsed electrical noise signals are generated by means of a suitable electroacoustic transducer. Although an electroacoustic transducer is shown as the preferred acoustic generator, other types of mechanical driving systems (vibrators) could be used as alternatives. Pneumatic, hydraulic, and eccentric motor type vibrators are commonly available and they are all capable of generating an acoustic signal when adequately coupled to the water.

However, such vibrators are difficult or impossible to pulse rapidly enough for the present purposes so that they are not generally suitable. When water is pumped rapidly down a submerged tube it is possible to generate considerable acoustic energy by modulating the flow rate with an electrically driven control valve. Various problems associated with the modulated flow hydraulic acoustic generator make it generally impractical, however, but of possible use in shallow water. As an alternative to the submerged electroacoustic transducer shown, it is possible to couple the acoustic energy into the ocean by means of a water filled tube. Thus the electroacoustic transducer (sound projector) 9 and could be coupled into a water filled chamber aboard a vessel and the acoustic energy transmitted down a water filled tube extending from the chamber down to the desired depth. However, certain practical problems are encountered when transmitting acoustic signals down a tube in this manner. Therefore a submerged electroacoustic transducer connected to the surface by electrical conductors, is preferred as an acoustic generator for the fish attracting apparatus.

Although preferred forms of the invention have been described and illustrated herein, it will be understood that the invention may be embodied in other forms coming within the scope and meaning of the appended claims.

We claim:

1. Apparatus for attracting fish by means of acoustic signals transmitted into the water comprising: an electrical signal generator having an output waveform substantially high in harmonic content and a fundamental frequency within the range of l to 700' c./s.; means for amplifying electrical signals from the said signal generator; an electroacoustic transducer for transmitting acoustic signals into water in response to electrical signals from the said amplifier, the said transducer being responsive over at least a portion of the aforementioned range of frequencies; and means of intermittently varying the amplitude of the aforementioned electrical signals to form a series of pulses.

2. Apparatus as described in claim 1 wherein the said electrical signal generator is an oscillator providing a substantially rectangular waveform rich in odd harmonics.

3. Apparatus for attracting fish by means of acoustic signals transmitted into the ocean comprising in combination: means for generating an electrical noise signal having at least a narrow band of frequency components within the range of 10 cycles per second to 700 cycles per second; means for amplifying the said electrical noise signal; means for intermittently varying the amplitude of the said noise signal to form a series of pulses; and means for transmitting acoustic pulses into the sea corresponding to the said amplified and pulsed electrical noise signals.

4. Apparatus as described in claim 3 wherein the said electrical noise signal generator is a random noise generator and filter combination for providing a band of noise within the aforementioned frequency range.

5. The method of attracting predatory fish which comprises: transmitting an acoustic signal into the sea having frequency components within the range of 10 c./s. to 700 c./s.; and intermittently varying the amplitude of the said acoustic signal so that a series of acoustic pulses result, the said acoustic pulses having frequency components and an amplitude variability which simulate the hydrodynamic sounds generated by spasmotic fish movements.

References Cited UNITED STATES PATENTS RICHARD A. FARLEY, Primary Examiner. 

